GENUS STENTOR. 589 



tation, which gives off" an horizontal annular branch which underlies the 

 circumference of the peristome, and a canal-like diverticulum which is con- 

 tinued towards the posterior extremity of the body. Increasing by oblique 

 fission, and by germs separated from the band-like endoplast. Inhabiting 

 fresh and salt water ; mostly social. 



The Stentors or trumpet animalcules represent, by reason of their large 

 dimensions, social habits, often brilliant colouring, and cosmopolitan distribution, 

 not only the most familiar but the very earliest known members of their class. 

 The first record of the group is given by our illustrious countryman Abraham 

 Trembley, noted chiefly for his researches connected with the fresh-water polypes 

 Hydra vulgaris and ff. viridis, and who, premising that these animalcules possessed 

 a closely identical organization, described them under the tide of the " Funnel-like 

 Polypes" in the 'Philosophical Transactions' for the year 1744. Three modifi- 

 cations of this so-called polj^je were observed by this early investigator, and dis- 

 tinguished by him under the names of the "green," " blue," and "white" varieties, 

 the same evidently corresponding with the three types familiar to recent investi- 

 gators under the respective technical appellations of Stcntor polymorphus, S. ccBrulcus, 

 S. Ra:selii. In Mr. Baker's treatise, a few years later, ' EmpIo>'ment for the Micro- 

 scope,' 1753, these several varieties recur under the title of the "Funnel Animal," 

 while one of them, S. Hceselii, is included in Linnsus's 'Systema Nature,' 

 ed. X., 1758, under the name of Hydra steniorca. The first employment of the 

 generic title of Stetttor was made by Oken,* 18 15, who, however, included under the 

 same generic category the totally dissimilar organisms Ophydium versatile and the 

 social Rotifer Lacimilaria. By O. F. Miiller numerous representatives of the genus 

 are embodied in his comprehensive generic group Vorticella, Ehrenberg being the 

 first to secure to the genus Stenior that well-defined limitation by wiiich, from then 

 up to the present time, it has been distinguished. 



A iioteworthy feature connected with the life-history of the representatives of this 

 genus is afforded by their mode of multiplication by fission, and which, instead of 

 taking a transverse or longitudinal direction, as in almost all other animalcules, 

 describes an oblique course. The phenomena accompan>ing this duplicative process 

 are of much interest, and were first recorded in a manner leaving but little to be added 

 by Trembley, their first discoverer. The eariiest indications given of the impending 

 subdivision is the appearance down that side of the body of the animalcule which 

 accords with the one on which the peristome makes its spiral descent into the oral 

 aperture, and may be hence termed the ventral aspect, of a raised crest or border, which 

 in its eariiest condition presents the appearance of an undulating membrane, but sub- 

 sequently splits up and forms a fringe of long cirrhate cilia similar to those which bound 

 the expanded peristome. Up to within a comparatively recent date this lateral crest 

 or fringe has been regarded as a permanent and distinctive feature of the type with 

 which it has been seen associated, and is cited in Pritchard's ' Infusoria ' as largely 

 developed in certain species, slightly only in others, while in a third series it is alto- 

 gether wanting. By Stein, Claparfede and Lachmann, and numerous other observers, 

 including among our own countr)'men Dr. W. Moxon,t it has, however, been cleariy 

 demonstrated that this lateral crest represents the i-udimentary condition only of 

 the adoral or peristomal fringe of cilia of the posteriorly-produced zooid or resultant 

 of the process of segmentation, and which gradually shapes itself so as to corre- 

 spond in form and character with that of the pre-existing anterior adoral wreath as 

 follows. In the first place the simple lateral crest or line of cilia becomes spirally in- 

 volute at its lower or proximal extremity, and, penetrating in a conical form into the 

 substance of the parenchyma, forms the oral aperture of the new zooid now in course 

 of development This oral aperture, with its simple linear fringe of adoral cilia, may 

 be said at this particular stage of development to correspond closely with the normal 



* ' Lehrbuch der Naturgeschichte,' Th. iii. 



t ' Journal of Anatomy and Physiology,' May, 1869. 



